General-purpose engines are predominantly gasoline engines having a spark plug. A generator is provided to a general-purpose engine due to a need to supply power to a spark plug and other electrical components. Since general-purpose engines are generally small, small generators are also used, as described in Japanese Patent Application Laid-Open Publication No. 2007-6594 (JP 2007-6594 A).
FIG. 5 hereof shows a generator disclosed in JP 2007-6594 A. A generator 100 has a stator provided with a coil 102, and a rotor provided with a magnet 101 which rotates relative to the stator. A flywheel 104 is mounted to an end of a crankshaft 103. The flywheel 104 has a hub spindle 105 fitted to the tapered part of the crankshaft 103, a disk part 106 extended radially outward from the hub spindle 105, and an outer-mass part 107 formed integrally with the outer circumference of the disk part 106. Since the outer-mass part 107 has a large mass and is distant from the center (rotational center) of the crankshaft 103, the moment of inertia (the moment of inertia is proportional to mass×distance2) is also large, and the flywheel effect is considerable.
The magnet 101 is provided to the outer-mass part 107. For this reason, the magnet 101 is a ring magnet having a large diameter. The magnet 101 is mounted to the outer-mass part 107 by holders 108, 108.
A disk-shaped iron core 111 wrapped in the coil 102 is secured to a crankcase 113 by bolts 112, 112.
When the crankshaft 103 rotates, electrical generation begins because the magnet 101 rotates relative to the coil 102.
The magnet 101 must be fitted to the outer-mass part 107 and held in place by the holders 108 on both sides. The holders 108 are needed to prevent the magnet 101 from being separated from the outer-mass part 107 by vibration. However, the magnet 101 is fitted to the outer-mass part 107 and the holder 108 is then mounted, making it more complex to mount the magnet. A complex mounting process results in a greater number of assembly steps and is undesirable. In view of this, a simplified process for mounting the magnet is needed.
The magnet 101 has a large diameter, and hence a greater mass, making the magnetic generator 100 large and heavy. Considering that the generator is attached to a small general-purpose engine, a reduction in the size and weight of the generator is sought.